Plasmodium falciparum sporozoite loads in Anopheles gambiae s.l. across agro-ecological zones of Benin: a cross-sectional field study.

Abstract

BACKGROUND: Malaria transmission depends critically on the vectorial competence of Anopheles mosquitoes, which is partly reflected by the quantity of infectious Plasmodium falciparum forms harboured in the salivary glands. Whether agro-ecological heterogeneity and vector species identity modulate this parasite burden remains poorly characterized in Benin. METHODS: Anopheles gambiae s.l. were collected by Human Landing Catch across 12 localities spanning 7 agro-ecological zones in Benin during August-October 2022. Species were identified by SINE-PCR. P. falciparum infection was assessed by circumsporozoite protein (CSP) ELISA, and sporozoite load was quantified in positive head-thorax preparations by real-time PCR targeting the plasmepsin gene (NZYTech kit, ref. MD 02411). Statistical comparisons across agro-ecological zones (within each species) used the Kruskal-Wallis test, and the two-species comparison used the Mann-Whitney U test, in R v4.4.1. RESULTS: A total of 1,355 individuals were molecularly analyzed for species identification. Of 3,021 mosquitoes collected, these 1,355 yielded 858 An. coluzzii (63.32%), 489 An. gambiae (36.09%), and 8 An. arabiensis (0.59%). The overall sporozoite index was 5.98% (95% CI 4.8-7.4%), ranging from 0% in Cotonou and Parakou to 16.19% in Boukoumb&#xe9;. No significant inter-zonal variation in sporozoite load was detected in either An. coluzzii (Kruskal-Wallis: H&#x2009;=&#x2009;5.79, df&#x2009;=&#x2009;3, p&#x2009;=&#x2009;0.122) or An. gambiae (H&#x2009;=&#x2009;3.25, df&#x2009;=&#x2009;2, p&#x2009;=&#x2009;0.197). However, An. coluzzii carried a significantly higher sporozoite burden than An. gambiae (Mann-Whitney U&#x2009;=&#x2009;381, p&#x2009;<&#x2009;0.001). CONCLUSIONS: Broad agro-ecological zone categories were not associated with detectable differences in individual P. falciparum sporozoite load in the principal malaria vectors of Benin. Anopheles coluzzii carried a significantly higher sporozoite burden than An. gambiae, indicating species-level differences in parasite permissiveness that merit further investigation.